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The only issue with this is the godzilla fin that both magikarp and gyarados have, along with their tail fin.
I think it's more accurate to say that Dragonite was it's own Pokemon later retrofitted into the Dratini line. Either that or they somehow fucked up and switched Gyarados and Dragonite's colors. Who knows with GameFreak, they made a lot of weird decisions during Alpha/Beta of Gen 1, and some they didn't even bother to fix (such as Wartortle/Blastoise originally being two separate lines that got smashed together).